Nature isn't an arbiter of truth, it's a publisher of papers. It's also meant to be read critically by people who see a paper like this and and think "interesting, but this is just an observational study, I'd like to see more research, maybe something with more controls before I believe this".

Say what you want about the "correlation doesn't imply causation", but many people do not understand why that is. As a shorthand for "hey, you don't know the statistics behind this, so don't take the pretty picture at face value", it's pretty good.